The Effect of Cu²⁺ Substitution on the Properties of BNKLT Lead-Free Ceramics Fabricated by the Solid-State Combustion Technique

Abstract

This article reports the effect of Cu²⁺ substitution on the phase formation, morphology and electrical behavior of Bi_0.5Na_0.34K_0.11Li_0.05Ti_(1-x)Cu_xO₃ with 0 ≤ x ≤ 0.020 (BNKLT-xCu) ceramics prepared by the solid state combustion technique with glycine used as the fuel. All samples were prepared with a calcination temperature and a sintering temperature of 750 °C and 1025 °C, respectively for 2 h. The XRD results of all compositions revealed a single perovskite structure and that Cu²⁺ diffused efficiently into B-sites of the lattice, producing a BNKLT-xCu solid solution. The phase formation of the BNKLT-xCu ceramics showed coexisting rhombohedral (R) and tetragonal (T) phases in all samples. The highest measured density of the BNKLT ceramics was 5.99 g/cm³ and good dielectric properties measured at the temperature of the maximum dielectric constant (ε_m = 4723 and tanδ = 0.054), were obtained by the sample with Cu²⁺ substituted at x = 0.010. The BNKLT-xCu ceramics with Cu²⁺ ≥ 0.005 showed pinched P-E loops, and the negative strain of the S-E loops started to disappear, owing to the Cu²⁺ induced transformation from the ferroelectric (FE) phase to the ergodic relaxor (ER) phase. With Cu²⁺ levels of 0.010, the d*₃₃ value increased to 705 pm/V, indicating that this sample was near the FE–ER phase boundary with induced high strain. Substituting an appropriate amount of Cu²⁺ improved the densification of BNKLT-xCu ceramics as capillary forces in the liquid phase during sintering pulled the grains together, which increased the ε_m values.

Keywords:

• BNKLT-xCu ceramics
• solid-state combustion technique
• dielectric behavior
• ferroelectric properties

Acknowledgements

The authors wish to thank the Department of Physics, Faculty of Science, Naresuan University for their supporting facilities. Thanks are also given to Dr. Kyle V. Lopin for his help in editing the manuscript.